Thanks very much for the screen recording. I can see why you'd think that the problem happens with any stock photo, but the issue actually isn't with photos at all.
That message
only applies to video clips, and I'm virtually certain that you're seeing it because at least one previously downloaded video clip - most likely a QuickTime clip that ends with .mov - is present when PD opens up the Downloaded content library.
You can verify this by closing PD, then reopen it and click on the Downloaded tab without downloading any new clips. I expect you'll see the message again.
If that's the case, the error message keeps popping up because your system isn't configured properly to work with .mov clips. You can either remove all the downloaded .mov clips (right click on each and choose Delete From Disk) or download and install the free QT Lite codec. See this
discussion for more info.